Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07D—HETEROCYCLIC COMPOUNDS
  • C07D263/00—Heterocyclic compounds containing 1,3-oxazole or hydrogenated 1,3-oxazole rings
  • C07D263/02—Heterocyclic compounds containing 1,3-oxazole or hydrogenated 1,3-oxazole rings not condensed with other rings
  • C07D263/04—Heterocyclic compounds containing 1,3-oxazole or hydrogenated 1,3-oxazole rings not condensed with other rings having no double bonds between ring members or between ring members and non-ring members
  • C07D263/06—Heterocyclic compounds containing 1,3-oxazole or hydrogenated 1,3-oxazole rings not condensed with other rings having no double bonds between ring members or between ring members and non-ring members with hydrocarbon radicals, substituted by oxygen atoms, attached to ring carbon atoms
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61P—SPECIFIC THERAPEUTIC ACTIVITY OF CHEMICAL COMPOUNDS OR MEDICINAL PREPARATIONS
  • A61P35/00—Antineoplastic agents
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07D—HETEROCYCLIC COMPOUNDS
  • C07D493/00—Heterocyclic compounds containing oxygen atoms as the only ring hetero atoms in the condensed system
  • C07D493/02—Heterocyclic compounds containing oxygen atoms as the only ring hetero atoms in the condensed system in which the condensed system contains two hetero rings
  • C07D493/08—Bridged systems

Definitions

• the present application generally relates to process for the preparation of taxane derivatives useful in the treatment of cancer in patients and to intermediates useful in such processes. More particularly this application relates to processes useful inter alia in the preparation of paclitaxel, docetaxel and to certain 9,10- ⁇ , ⁇ -OH taxane analogues having a bridge between the 7-OH and 9-OH groups.
• Paclitaxel and docetaxel are well established anticancer agents for which numerous synthetic methods are known. Methods of synthesis of certain 9,10- ⁇ , ⁇ OH taxane analogues are disclosed in WO 2005/030152. Other synthetic methods are disclosed in EP 1 228 759 A (Florida State University), EP 1 285 920 A (Florida State University), EP 1 148 055 A (Florida State University), WO 01/56564 A (Florida State University), WO 01/57027 (Florida State University), WO 94/10996 A (Florida State University), FR 2 715 846 A (Rhone-Poulenc), U.S. Pat. No.
• paclitaxel and docetaxel and other taxane derivatives involve the use of a ⁇ -lactam to acylate the ⁇ -hydroxy group of a 10-baccatin III or a 10-deacetylbaccatin III derivative.
• Other methods have described the coupling of a carboxylic acid to 10-baccatin III or a 10-deacetylbaccatin III, for example with DCC.
• WO 2005/03150 discloses an improved process for coupling certain side chains to the ⁇ -hydroxy group of taxane variants by using an acyl fluoride.
• the numbering system of the taxane backbone is:
• paclitaxel appears promising as a chemotherapeutic agent, chemists have spent substantial time and resources in attempting to synthesize paclitaxel and other potent taxane analogs.
• the straightforward implementation of the partial synthesis of paclitaxel or other taxanes requires convenient access to chiral, non-racemic side chains and derivatives, an abundant natural source of baccatin III or closely related diterpenoid substances, and an effective means of joining the two units.
• Perhaps the most direct synthesis of paclitaxel is the condensation of Baccatin III and 10-deacetylbaccatin III of the formula:
• P 1 is a hydroxyl protecting group, with a taxane derivative of the general formula:
• P 2 is a hydroxyl protecting group.
• the condensation product is subsequently processed to remove the P 1 and P 2 protecting groups.
• the paclitaxel C-13 side chain, (2R,3S)3-phenylisoserine derivative is protected with P 1 for coupling with a protected Baccatin III.
• the P 2 protecting group on the baccatin III backbone is, for example, a trimethylsilyl or a trialkylsilyl radical.
• R 1 is alkyl, olefinic or aromatic or PhCH 2 and P 1 is a hydroxyl protecting group.
• docetaxel is similar to paclitaxel except for the t-butoxycarbonyl (t-Boc) group at the C3′ nitrogen position of the phenylisoserine side chain and a free hydroxyl group at the C10 position. Similar to paclitaxel, the synthesis of docetaxel is difficult due to the hindered C13 hydroxyl in the baccatin III backbone, which is located within the concave region of the hemispherical taxane skeleton.
• t-Boc t-butoxycarbonyl
• This application provides an effective synthesis of taxane derivatives by esterifying a 13-OH group of a taxane derivative with a cyclically protected side chain acid and thereafter removing the protecting groups.
• R 1 and R 2 are independently H or substituted or unsubstituted alkyl, alkenyl, aryl, aralkyl or acyl;
• R 3 is H or P 1 where P 1 is an amino protection group;
• X is halogen or OR 4 where R 4 is H, a substituted or unsubstituted alkyl, alkenyl, aryl, aralkyl, acyl, acyloxycarbonyl or aryloxycarbonyl;
• X 2 is substituted or unsubstituted alkyl, alkenyl, aryl, aralkyl or acyl;
• Y 7 is R 7 , P 3 or Z 7 ;
• Y 9 is H, OH, a ketone, OR 9 , P 4 or Z 9 ;
• Y 10 is R 10 , P 5 or Z 10 ;
• R 7 is H, substituted or unsubstituted alkyl, alkenyl, aryl, aralkyl or acyl; Z 7 is P 3 and together with Y 9 forms a cyclic structure when Y 9 is P 4 ; Z 9 is either R 9 and together with Y 7 forms a cyclic structure when Y 7 is P 3 ; or Z 10 is P 5 and together with Y 9 forms a cyclic structure when Y 9 is P 4 ; P 5 and together with Y 10 forms a cyclic structure when Y 10 is P 4 ; R 9 is a substituted or unsubstituted alkyl, alkenyl, aryl, aralkyl or acyl; R 10 is H, substituted or unsubstituted alkyl, alkenyl, aryl, aralkyl or acyl; P 3 is a hydroxyl protecting group; P 4 is a hydroxyl protecting group; and P 5 is a hydroxyl protecting group and thereafter
• X is OR 4 ;
• X 2 is isobutyl;
• Y 7 is P 3 ;
• Y 9 is a ketone;
• Y 10 is P 5 ;
• R 1 is H;
• R 4 is H;
• P 1 is Boc;
• P 2 is BOM;
• P 3 is Cbz; and
• P 5 is Cbz.
• X is a halogen
• X 2 is isobutyl
• Y 7 is P 3
• Y 9 is a ketone
• Y 10 is P 5
• R 1 and R 2 are independently H or substituted or unsubstituted: alkyl, alkenyl, aryl, aralkyl, or acyl
• R 3 is H
• P 1 is Boc
• P 2 is BOM
• P 3 is Cbz
• P 5 is Cbz.
• the benzoxycarbonyl group is frequently a preferred protecting group to use.
• the application also provides particularly apt protected side chain acids for use in the process. These are of the formula (I):
• a 1 is hydrogen, halogen, lower alkyl or lower alkoxy
• a 2 is hydrogen, halogen, lower alkyl or lower alkoxy
• a 3 is BOC; Cbz or PhCO;
• R 1 is lower alkyl or phenyl
• alkyl as used herein alone or as part of another group, denotes optionally substituted, straight and branched chain saturated hydrocarbon groups, preferably having 1 to 12 carbons in the normal chain.
• substituted aryl refers to an aryl group substituted by, for example, one to four substituents such as alkyl; substituted alkyl, halo, trifluoromethoxy, trifluoromethyl, hydroxy, alkoxy, cycloalkyloxy, heterocyclooxy, alkanoyl, alkanoyloxy, amino, alkylamino, aralkylamino, cycloalkylamino, heterocycloamino, dialkylamino, alkanoylamino, thiol, alkylthio, cycloalkylthio, heterocyclothio, ureido, nitro, cyano, carboxy, carboxyalkyl, carbamyl, alkoxycarbonyl, alkylthiono, arylthiono, alkysulfonyl, sulfonamido, aryloxy and the like.
• the substituent may be further substituted by halo,
• aralkyl refers to alkyl groups as discussed above having an aryl substituent, such as benzyl or phenethyl, or naphthylpropyl, or an aryl as defined above.
• acyl denotes the moiety formed by removal of the hydroxyl group from the group —COOH of an organic carboxylic acid.
• the acyl group can specifically be PhCO or BnCO, for example.
• Exemplary hydroxyl protecting groups include methoxymethyl, 1-ethoxyethyl, 1-methoxy-1-methylethyl, benzyloxymethyl, ( ⁇ -trimethylsilyl-ethoxy)methyl, tetrahydropyranyl, benzyloxycarbonyl, 2,2,2-tri-chloroethoxycarbonyl, t-butyl(diphenyl)silyl, trialkylsilyl, trichloromethoxycarbonyl, and 2,2,2-trichloroethoxymethyl.
• Exemplary amine protecting groups are acyl, including formyl, acetyl, chloroacetyl, trichloroacetyl, O-nitrophenylacetyl, o-nitrophenoxyacetyl, trifluoroacetyl, acetoacetyl, 4-chlorobutyryl, isobutyryl, o-nitrocinnamoyl, picolinoyl, acylisothiocyanate, aminocaproyl, benzoyl and the like, and acyloxy including methoxycarbonyl, 9-fluorenylmethoxycarbonyl, 2,2,2-trifluoroethoxycarbonyl, 2-trimethylsilylethoxycarbonyl, vinyloxycarbonyl, allyloxycarbonyl, t-butyloxycarbonyl (BOC), 1,1-dimethylpropynyloxycarbonyl, benzyloxycarbonyl (CBZ), p-nitrobenzyloxycarbonyl, 2,
• halogen as used herein alone or as part of another group, denotes chlorine, bromine, fluorine, and iodine of which fluorine and chlorine are preferred.
• a 1 is hydrogen, halogen, lower alkyl or lower alkoxy
• a 2 is hydrogen, halogen, lower alkyl or lower alkoxy
• a 3 is BOC, Cbz or COPh
• the compounds of formula (I) have been found to be particularly effective agents for esterifying the 13-OH group of the taxane nucleus. Additionally, it has been found that removal of the protective moiety after coupling can be carried out without causing undesired epimerization of the side chain, for example by hydrogenation, for example employing a palladium or charcoal catalyst.
• lower means up to 6 carbon atoms, more aptly up to 4 carbon atoms.
• lower alkyl can be methyl to hexyl, more aptly methyl, ethyl, propyl or butyl and is preferably methyl.
• lower alkoxy can be methoxy to hexyloxy, more aptly methoxy to butoxy and preferably methoxy.
• the most apt halogens are chloride and fluorine of which fluorine is preferred.
• a 2 is preferably a hydrogen atom.
• a 1 is favourably a methoxy group, especially a 4- or 6-methoxy group and preferably a 6-methoxy group.
• R 1 is favorably an iso-butyl group i.e. a (CH 3 ) 2 CHCH 2 — group.
• R 2 is a group such that OCOR 2 is readily displaceable on reaction with an hydroxy group or metal alkoxide group.
• the 13-OH group of the taxane derivative does not become acylated to any wasteful extent by acylation by the COR 2 moiety when the compound of the formulas (I), (II), (III), (IV) or (V) is employed as an acylating agent.
• An acid chloride or acid fluoride analogous to the above mixed compounds may also be employed but this has been found to be less advantageous than the use of the above mixed anhydrides.
• R 2 is the t-butyl group. This can be prepared from the corresponding acid and pivaloyl chloride (CH 3 ) 3 CCOCl, for example in situ prior to the acylation of the 13-OH group.
• R 2 groups include lower alkyl, lower aralkyl and aryl groups.
• the group R 2 is aptly a voluminous group, for example a tertiary alkyl group or an electron withdrawing group so that the ⁇ OCOR 2 anion is stabilised.
• other apt groups R 2 include benzhydril, trityl, phenyl, 2,4-dichlorophenyl, 2,6-dichlorophenyl, 2,6-di-tert-butyl-phenyl, 4-nitrophenyl and the like.
• the acids corresponding to compounds of the formula (I) may be prepared by the oxidation of a compound of the formula (VII):
• a 1 , A 2 , A 3 and R 1 are as defined in relation to formulas (I)-(V). This may be effected by conventional mild vinylic oxidation reagents for example. NaIO 4 , OsO 4 , NMO, TPAP, ozone etc.
• the compound of the formula (VII) may be prepared by the following sequence:
• This process is particularly useful in the preparation of the compound of formula (VI) by using 2,6-dimethoxybenzaldehyde.
• the compound of the formula (VI) (and other carboxyl acids as referred to above) may be converted into the acid chloride or acid fluoride in conventional manner.
• a particularly favoured method of preparing an acid fluoride is by reaction with (CH 3 CH 2 ) 2 N—SF 3 or deoxofluor, for example in pyridine and dichloromethane.
• Such acyl fluorides may be, reacted with the 13-OH group of a taxane derivative in, for example, dichloromethane or tetrahydrofuran with a base, for e.g., DMAP, DBU etc.
• a base for e.g., DMAP, DBU etc.
• the preparation of the compound of formula (I) from the analogous acid is generally carried out under an inert atmosphere, for example nitrogen, at a non-extreme temperature, for example an ambient temperature of 15-25° C.
• a non-hydroxylic solvent is employed, for example, tetrahydrofuran.
• a tertiary amine for example N-methylmorpholine, is employed as proton acceptor.
• pivaloyl chloride or other compound of the formula ClCOR 2
• the reaction mixture allowed to stir at ambient temperature until complete (as indicated by HPLC).
• dilute acid may be employed.
• the solution may be cooled to about ⁇ 18° C. to ⁇ 20° C. and 0.5N HCL in methanol employed.
• the mixture may then be stirred at a depressed temperature, for example ⁇ 15° C., until deprotection is complete (as indicated by HPLC).
• the reaction may then be quenched, for example 5% sodium bicarbonate solution) and concentrated by evaporation before yielding the product.
• the backbone hydroxyl group(s) can be protected by using a protecting group which is readily cleavable with acid so that a single deprotecting reagent is employed. Also, the backbone hydroxyl group(s) can be protected with a group readily removable by hydrogenation, for example a Cbz group.
• hydrogenation may be effected in conventional manner, for example employing 10% Pd/C catalyst in a THF, an aqueous THF or methanolic solution, followed by an acidification, for example with formic or acetic acid, for example in methanol.
• a hydrogenation reaction could be employed when A 3 is a Cbz group so that a deprotected primary amino group could be produced in the side chain which could be thereafter acylated to provide a benzoyl or BOC substituted amino group if desired.
• Favoured compounds of the formula (XVII) include those wherein A 4 is a hydrogen atom or is a hydroxyl protecting group selected from the groups consisting of benzyl, Cbz or acetyl group, preferably an acetyl and A 4 is in the ⁇ configuration, and A 5 is joined to A 6 to form an O—CH(CH ⁇ CH 2 )—O moiety and A 5 is in the ⁇ configuration.
• Compounds of the formula (XVII) are particularly apt for use in the preparation of paclitaxel, docetaxel or TPI287. Such compounds may be deprotected by acidification. Such compounds containing a Cbz group may be deprotected by hydrogenation. If such hydrogenation replaces a A 3 group which is Cbz by hydrogen, that compound may be acylated to yield one which contains a PhCO or BOC group, for example by reaction with the appropriate anhydride or acyl halide.
• R 1 and R 2 are independently H or substituted or unsubstituted alkyl, alkenyl; aryl, aralkyl or acyl; R 3 is H or P 1 where P 1 is an amino protection group;
• X is halogen or OR 4 where R 4 is H, a substituted or unsubstituted alkyl, alkenyl, aryl, aralkyl, acyl, acyloxycarbonyl or aryloxycarbonyl;
• X 2 is substituted or unsubstituted alkyl, alkenyl, aryl, aralkyl or acyl;
• Y 7 is R 7 , P 3 or Z 7 ;
• Y 9 is H, OH, a ketone, OR 9 , P 4 or Z 9 ;
• Y 10 is R 10 , P 5 or Z 10 ;
• R 7 is H, substituted or unsubstituted alkyl, alkenyl, aryl, aralkyl or acyl; Z 7 is P 3 and together with Y 9 forms a cyclic structure when Y 9 is P 4 ; Z 9 is either R 9 and together with Y 7 forms a cyclic structure when Y 7 is P 3 ; or Z 10 is P 5 and together with Y 9 form a cyclic structure when Y 9 is P 4 P 5 and together with Y 9 forms a cyclic structure when Y 10 is P 4 ; R 9 is a substituted or unsubstituted alkyl, alkenyl, aryl, aralkyl or acyl; R 10 is H, substituted or unsubstituted alkyl, alkenyl, aryl, aralkyl or acyl; P 3 is a hydroxyl protecting group; P 4 is a hydroxyl protecting group; and P 5 is a hydroxyl protecting group.
• X may be fluorine or chlorine but is preferably OCOR 2 as defined in relation to formula (I), in particular a OCOC(CH 3 ) 3 group.
• X may be a leaving group such as bromine, azide etc.
• X 2 is phenyl or CH 2 CH(CH 3 ) 2 ;
• R 5 is (CH 3 ) 3 CO, Ph or PhO;
• R 1 and R 2 are independently hydrogen, lower alkyl, lower alkyl substituted by lower alkoxy, phenyl or phenyl substituted by one, two or three groups selected from lower alkyl, lower alkoxy, fluorine or chlorine.
• R 1 is hydrogen.
• R 2 is an optionally substituted phenyl group.
• R 2 is a group of the formula
• a 1 and A 2 are as defined above.
• the compound of the formula (X) is aptly of the formula (XII) or (XIII):
• Y 11 is hydrogen or a hydroxyl protecting group, such as a Cbz group and Y 12 is a hydrogen atom or a protecting group such as a Cbz or acetyl group.
• Y 11 is favourably a group removable by hydrogenation and is preferably a Cbz group.
• R 1 , R 2 , R 5 , X 2 , Y 11 and Y 12 are as defined herein before. Such compounds are useful as intermediates in the synthesis of paclitaxel and docetaxel.
• R 1 , R 2 , R 5 and X 2 are as defined above.
• X 2 , R 3 , Y 10 , Y 9 and Y 7 are as defined in relation to formula (VIII) which comprises deprotection of the side chain moiety in the compounds of formula (VIII), preferably by treatment with acid, for example formic acid, acetic acid or aqueous HCl in methanolic solution.
• acid for example formic acid, acetic acid or aqueous HCl in methanolic solution.
• FIGS. 1, 2 and 3 Suitable sequences are shown in FIGS. 1, 2 and 3:
• the 9-keto alcohol 1 is selectively oxidized to form the 9,10-di-keto 2:
• the di-keto 2 may be obtained as a mixture of the di-keto, 2a and 2b.
• the two isomers, 2a and 2b may be separated to afford 2a, or the mixture may be used as is in the subsequent step without separation.
• the mixture may be derivatized to form the corresponding protected alcohol, and a number of applicable alcohol protecting groups are disclosed, for example, in T. W. Greene and P. G. M. Wuts, Protective Groups in Organic Synthesis, 3rd Edition, John Wiley & Sons, New York (1999).
• the mixture is derivatized to form the corresponding protected silyl ether, such as the triethylsilyl ether, such as by treating the mixture with TES-OTf (trifluoromethanesulfonic acid triethylsilylester), pyridine and solvents like NMP to form the 7,13-di-silyl ether 3.
• TES-OTf trifluoromethanesulfonic acid triethylsilylester
• pyridine triethylsilylester
• solvents like NMP solvents like NMP
• the undesired isomer 2b may be separated from the desired isomer 2a using various methods known in the art, including column chromatography and crystallization.
• the epimeric isomers of the corresponding di-silyl ether 3 obtained may be separated using standard procedures known in the art. Because the isomer 2b forms the di-TES ether at a slower rate than the isomer 2a, the reaction condition may be adjusted accordingly to favor the formation of the isomer 2a.
• the di-silyl ether 3 may be reduced to the corresponding 9,10-di-ol 4.
• Reduction may be performed using a hydride reducing agent, such as using NaBH 4 in an organic solvent.
• reduction of the di-ketone may be accomplished using LiBH 4 in a solvent or solvent mixture, such as THF/EtOH to form the di-ol 4.
• the reaction may be performed at room temperature, or below room temperature, or at about 20° C. to about ⁇ 10° C., more preferably at about 0° C.
• the di-ol 4 is converted to the corresponding 10-acylated alcohol 5 using an acylation agent such as acetic anhydride, TEA, DMAP and IPAC, to form the 10-acylated alcohol 5.
• an acylation agent such as acetic anhydride, TEA, DMAP and IPAC
• Selective hydrolysis of the TES groups may be accomplished using, for example, AcOH in MeOH/H 2 O, or using IPAc/MeOH, to afford the tetra-ol 6.
• Acetalization of the 7,9-di-ol of compound 6, preferably using acrolein diethyl acetal in an organic solvent, such as toluene, and TFA in an ice bath provides the allylidene acetal 7 in good yields.
• Coupling of the allylidene acetal 7 with the acid 8a affords the coupled product 9a.
• Deprotection affords compound 10 (TPI287) in good yields.
• coupling reaction of the allylidene acetal 7 with the acid 8 affords the coupled product 9, which is not isolated, and the N,O-acetal is hydrolyzed in situ, as provided herein affords the product, compound 10 (TPI287) in good yields.
• the hydrolysis may be performed using an acid in an alcohol at low temperatures, such as hydrochloric acid in methanol at about ⁇ 25° C. to 25° C., preferably about ⁇ 15° C.
• This general procedure may be employed using either of the starting isomer 8a or 8b, that forms the corresponding isomer 9a or 9b, respectively.
• the N,O-acetal 8b may be prepared according to the procedure illustrated in FIG. 4 to provide the desired product in good yield.
• the N,O-acetal isomer 8a may be prepared according to the procedure illustrated in FIG. 4 to provide the product in good yield.
• a method which can be adapted for preparing the intermediates in FIG. 4 is disclosed in the Journal of Organic Chemistry, 2001, 66, 3330-3337, the reference of which is incorporated herein in its entirety.
• the intermediates described herein may be isolated and/or purified in one or more processing step before submitting to the subsequent reaction step or steps.
• the subsequent reaction step or steps of a reaction product (or intermediate) is subjected to one or more subsequent reaction without isolation and/or purification until the final product compound 10 (TPI287) is obtained.
• purification of the intermediates and/or product may be performed using various methods known in the art, including column chromatography, crystallization, distillation and the like, or the combination of the methods.
• Standard procedures and chemical transformation and related methods are well known to one skilled in the art, and such methods and procedures have been described, for example, in standard references such as Fiesers' Reagents for Organic Synthesis , John Wiley and Sons, New York, N.Y., 2002; Organic Reactions , vols. 1-66, John Wiley and Sons, New York, N.Y., 2005; March J.: Advanced Organic Chemistry, 4th ed., John Wiley and Sons, New York, N.Y.; and R. C. Larock: Comprehensive Organic Transformations , Wiley-VCH Publishers, New York, 1999. All texts and references cited herein are incorporated by reference in their entirety.
• NMO NMO
• ACN 200 mL
• TPAP aqueous NaIO 4
• ACN 50 mL
• deionized water 50 mL
• TPAP 504 mg, 1.4 mmol
• a solution 16 (15.0 g, 38.3 mmol, 0.5 g/mL ACN) was added over the course of approximately 1 minute under ambient conditions.
• the sodium salt of the acid of formula (8a) may be obtained by the method of Bombardelli of al, WO 01/02407 or by neutralisation of the compound of Example 1.
• the mixed anhydride of formula (8c) is prepared and employed in situ as follows
• the coupled ester 9b was purified by flash chromatography on normal phase silica, eluting with an IPAc/n-heptane system of increasing polarity. Approximately 26 mg of the purified coupled ester was recovered as confirmed by LC/MS.
• the coupled ester (15 mg, 0.001 mmol) was dissolved into THF (1 mL). A 250 ⁇ L aliquot of the solution was diluted 1:1 with THF. The solution was stirred on an ice bath at ⁇ 0° C., after which HCl (0.5 N in MeOH, 25 ⁇ L) was added. The reaction was monitored by LC/MS, which indicated the formation of 10 (TPI 287).
• THF 1 mL
• Ammonium hydroxide (2M, 250 mL) was added and the reaction mixture was washed into a 4 L separatory funnel with water (250 mL) and EtOAc (300 mL). The mixture was further diluted with water (250 mL) and the layers were separated. The aqueous layer was back extracted with EtOAc (250 mL) and the organic layers were combined and washed with saturated ammonium chloride (3 ⁇ 250 mL). The organic layer was then washed with water (3 ⁇ ) and concentrated. Methanol (250 mL) was added, the mixture was stirred while heating to 50° C. for 1 hr. The mixture was then refrigerated for 2 hr, and filtered.
• the isolated product comprises approximately 10:1 to 20:1 of 2a to 2b.
• Triethylsilyl trifluoromethanesulfonate (TES-OTf) was added slowly to maintain the internal temperature at ⁇ 5° C. After the addition was complete, the flask was removed from the ice-bath. It was then placed in a warm-water bath and the reaction mixture was heated to 40° C. for ⁇ 6 hours. The flask was transferred back into an ice-water bath, cooled to 5° C. and water (100 mL) was added dropwise to quench the reaction. The mixture was transferred to a 2 L separatory funnel and diluted with IPAc, heptane and water. The layers were separated and the aqueous layer was re-extracted with IPAc and heptane.
• TES-OTf Triethylsilyl trifluoromethanesulfonate
• the solids were transferred to a 2 L flask equipped with a mechanical stirrer, thermocouple, addition funnel and N 2 stream (previously purged for 5 min).
• the solids in the rotovap flask were rinsed into the reaction flask with anhydrous pyridine (292 mL, 3 mL/g) and agitation was begun. Upon dissolution, agitation was continued and the contents of the flask were cooled to ⁇ 20° C.
• Triethylsilyl trifluoromethanesulfonate (120.9 mL, 3.0 eq) was slowly added to the reaction mixture to maintain the internal temperature of the reaction at ⁇ 10° C.
• Residues remaining in the reaction flask were washed into the separatory funnel with additional MTBE (200 mL, 2 mL/g), then water (250 mL, 2.5 mL/g) and saturated NH 4 Cl solution (250 mL, 2.5 mL/g) were added. The mixture was agitated and the layers were separated. The organic layer was transferred to a clean container. MTBE (250 mL, 2 mL/g) was added to the aqueous layer. It was agitated and the layers were separated. The second organic layer was washed into the first organic layer with MTBE (100 mL) and water (200 mL, 2 mL/g) was added to the combined layers.
• the reaction mixture was cooled to 19.7° C. and saturated ammonium chloride solution (552 mL) was added. After stirring for 15 min, the mixture was transferred to a separatory funnel, the layers were separated and the aqueous layer was removed. Water (280 mL) was added to the organic layer and the mixture was stirred for 4 min. The layers were again separated and the aqueous layer was removed. The organic layer was transferred to a 2 L rotovap flask and the remaining content of the separatory funnel was washed into the rotovap flask with IPAc (200 mL). The mixture was evaporated to dryness on the rotovap at 40° C. to give ⁇ 124 g 5 as pale yellow oily foam.
• the reaction was monitored by HPLC/TLC at 1-hour intervals for the disappearance of the starting material, formation and disappearance of the mono-TES intermediate and formation of the product 6.
• the reaction mixture was cooled to rt and transferred to a 10 L rotovap flask.
• Solvent exchanges to n-heptane (2 ⁇ 1370 mL, 1 ⁇ 1000 mL) and IPAc (2 ⁇ 1370 mL, 1 ⁇ 1500 mL) were performed.
• IPAc 280 mL, 2 mL/g
• silica 140 g, 1 g/g
• the dry silica mixture was loaded onto a silica pad (7 cm column, 280 g silica), conditioned with 2:1 n-heptane/IPAc (500 mL, 2 mL/g silica) and washed (4 ⁇ ) with 2:1 n-heptane/IPAc (2 mL/g silica, 3400 mL total). Each wash ( ⁇ 860 mL) was collected as a separate fraction and analyzed by TLC. The silica pad was again washed (4 ⁇ ) with 1:1 n-heptane/IPAc (3020 mL total, 2 mL/g silica) until all impurities were removed as indicated by TLC.
• Toluene (375 ml) was added to 6 (25 gm, 0.0424 mol) and cooled to ⁇ 15° C.
• TFA 9.8 ml, 3.0 eq
• the acrolein diethyl acetal (10.3 ml, 2.0 eq) was added and reaction was monitored every 30 min. Reaction was deemed complete when ⁇ 3% 6 remained.
• 1 g/g hydrated silica (25% water) was added to quench the reaction at ⁇ ⁇ 5° C.
• reaction mixture was analyzed by HPLC/TLC for consumption of starting material and formation of the coupled ester, 9a, at 30 min intervals beginning 30 min after the addition of the pivaloyl chloride.
• reaction was judged complete and the reaction mixture was cooled to 2° C.
• the reaction mixture was stirred at 2° C. ⁇ 2° C. and monitored by HPLC/TLC at 30 min intervals for consumption of 9a and formation of 10.
• the reaction was quenched with 5% aqueous sodium bicarbonate (300 mL) and IPAc (185 mL, 5 mL/g) was added.
• the reaction mixture was transferred to a 2 L rotovap flask and the reaction flask rinsed into the rotovap flask 2 ⁇ with 60 mL IPAc.
• the mixture was evaporated under vacuum at 40° C. until a mixture of oil and water was obtained.
• IPAc 200 mL was added to the oil and water mixture and the contents of the flask were transferred to a separatory funnel.
• the reaction flask was rinsed into the separatory funnel with IPAc (100 mL) and the contents of the separatory funnel were agitated and the layers were separated.
• the aqueous layer was removed. Water (70 mL) was added to the organic layer and, after agitation, the layers were separated and the aqueous layer was removed.

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